This invention relates to an apparatus for protecting the compressor casing and bleed manifold associated with a gas turbine engine from the deleterious effects of particles entrained in the gas stream of the gas turbine engine.
Gas turbine engines of modern vintage utilize lightweight materials, such as titanium as structural members in the construction of various components of the fan and compressor section of the engine. For instance, compressor rotors, rotor and stator airfoils, compressor casings and frames have all been constructed of titanium materials. These components have generally exhibited excellent performance and life characteristics during prolonged operation in the severe environment encountered in a gas turbine engine.
On extremely rare occasions, during the course of engine operation, abnormal conditions, such as fan blade, turbine blade or bearing failure, may cause high unbalance of the rotating components of the engine or in the case of failure of a titanium component a piece of Ti debris may lodge between the compressor rotating blade tip and the stator portion. In such an instance, rotating compressor blades may rub against their respective stationary casings or lodged Ti debris whereupon friction-generated heat and high internal engine pressure may cause titanium particles to ignite and burn. Molten, burning titanium particles may enter the high velocity gas flow stream for passage downstream.
Associated with compressor section of gas turbine engine, bleed manifolds are disposed adjacent bleed holes in the compressor for the purpose of drawing off pressurized air required by various mechanical systems on board the aircraft. The manifolds are generally constructed of relatively thin and unprotected walls which are particularly susceptible to the deleterious effects of the molten burning titanium particles. It has also been found that exposed titanium surfaces of the titanium compressor adjacent the bleed holes react with the entrained titanium particles and contribute to the deterioration of the manifold. More particularly, high velocity pressurized air, in which the titanium particles are entrained, impinges upon the exposed titanium surfaces of the compressor casing adjacent the bleed holes to cause the titanium casing to spontaneously ignite, melt and form additional incendiary titanium particles. These particles pass through the bleed holes and impinge upon and deteriorate the aforementioned thin-walled manifold.
Portions of the compressor casing other than the surfaces adjacent the bleed holes do not appear to be affected significantly by the molten titanium particles. This resistance is attributed to the fact that the internal surfaces of the compressor casing in the main gas stream flowpath are coated with various materials for the purpose of providing a relatively soft rub interface between the titanium casing and the rotating components of the compressor to avoid damage thereto and to provide a satisfactory gas seal necessary to avoid flow losses associated at the tips of the rotating blades. It has not previously been recognized that such coatings protect the titanium compressor casing from ignition by molten titanium particles nor has it even been recognized that the titanium casing requires such protection from ignition. This invention addresses the aforementioned problems by providing means for protecting the compressor casing and associated manifold in a number of complementary or alternative embodiments.